As devices performing cruise control of a vehicle, auto-cruise control and adaptive cruise control are disclosed in e.g., US 2004/0040765 (JP 2004-90712A) and U.S. Pat. No. 5,969,969 (JP 2003-272100A), respectively. The auto-cruise control allows a vehicle to travel at a driver-set vehicle speed, and the adaptive cruise control allows a vehicle to travel to follow a preceding vehicle while keeping a specific vehicular distance. Since a vehicle equipped with such cruise controllers eliminates the need for a driver to perform accelerator pedal and brake pedal operations, or reduces the number of the operations, the load of driving operations on the driver can be reduced.
Driving support control is also disclosed in JP 2000-211543A. This control does not perform the above cruise control but reduces the load of a steering operation, which is one of vehicle driving operations. This driving support control determines the degree of concentration of a driver on driving operations, and strengthens or relaxes the support of steering operation according to the concentration degree. That is, when the degree of concentration of the driver on driving operations is high, the need to support driving is little and support driving rather gives the driver a sense of incongruity, steering auxiliary force applied to a steering device of the vehicle to support driving is decreased. Conversely, when a concentration degree is low, steering auxiliary force is increased.
When a vehicle includes the above cruise control, although the load of a driver on driving operations can be reduced, the driver has overconfidence in the vehicle of being capable of driving even without performing operations by himself, so that attention to surrounding environments may be decreased. Particularly, when the cruise control last long, driver's attention may be distracted or lowered.
However, for example, when another vehicle traveling slower than the subject vehicle (own vehicle) changes laterally from an adjacent lane to the lane of the subject vehicle during the cruising at a fixed vehicle speed by cruise control, the driver must intervene in operations as required. Thus, during the cruise control, the driver must intervene in operations according to a change in surrounding environments. At this time, when the driver is low in concentration, a delay in recognition, judgment, and operations, and reduction in correctness may occur.
The above driving support control described in JP A-2000-211543 increases driving support in steering operations when the degree of concentration of the driver on driving operations is low. Therefore, even if the degree of concentration of the driver on driving operations is low, the vehicle can be controlled to travel a desired path. However, when a situation change that requires operation intervention by the driver occurs, again, a delay in recognition, judgment, and operations, and reduction in correctness may occur.